The use of light sources, such as lasers and other high intensity light devices, for dermatologic treatment and cosmetic applications is well known in the art. For example, applications for these light based devices include, but are not limited to, epilation for the removal of unwanted hair, hair-regrowth inhibition, tattoo removal, treatment of birthmarks, acne treatment, and facial resurfacing.
Examples of light-based systems for dermatological treatment and cosmetic applications are described in U.S. Pat. Nos. 4,232,678; 5,735,844; 5,885,273; 6,096,029; 6,197,020; 6,277,111; 6,508,813; 7,118,563; 7,250,045; 7,452,356; and 7,824,023, the disclosures of which are hereby incorporated by reference.
In general, two types of light-based cosmetic and treatment devices are marketed. A first market segment includes devices that are sold to physicians and treatment facilities. Examples of such products include the LightSheer diode laser system, manufactured by Lumenis Ltd.; the SLP-1000 fiber-coupled diode laser, available from Palomar Medical Technologies Inc.; the Quantum flash lamp system, manufactured by Lumenis Ltd., and the CoolGlide Excel YAG laser, available from Altus Inc.
A second market segment includes light-based devices sold directly to end-user consumers. One such device is the TRIA Laser Hair Removal System, manufactured by TRIA Beauty, Inc. The TRIA system is a hand-held device with an optical output portion that is placed in contact with the epidermis. Light from a diode laser is delivered to the skin to remove unwanted hair.
Many of the light-based devices sold in both market segments contact areas of the skin during treatment. Light from the light-source may be delivered through a lens or other form of optical output window (e.g., the LightSheer system). The optical output window may have an outer surface that contacts the epidermis.
Optical windows generally are made from materials that are appropriate for the dermatologic and/or cosmetic applications. Materials may be used such as sapphire, which in general has a high heat capacity and high thermal diffusivity. Also, sapphire use is particularly suitable for dermatologic and cosmetic applications because the refractive index of sapphire is near the refractive index of skin. In general, less light is reflected back away from the skin at a boundary of sapphire and skin than at other boundaries where skin contacts a material with a retractive index greater than the retractive index of sapphire.
Titanium dioxide (TiO2) has a refractive index between about 2.1 and 2.6. It is known that TiO2 has a photochemical property that enables the decomposition of various harmful substances, such as organic chemicals and microorganisms. Such decomposition occurs by oxidation, when the sapphire is exposed to ultraviolet light (UV light) (e.g., from sunlight, from fluorescent light sources) and reactive oxygen species are formed. This antimicrobial property of TiO2 can be further enhanced utilizing nitrogen doping. See M. Wong, et al., “Visible-light-Induced Bactericidal Activity of a Nitrogen-Doped Titanium Photocatalyst against Human Pathogens: Applied and Environmental Microbiology, p. 6111-6116, (September 2006).
The refractive index of TiO2 substantially exceeds the refractive index of skin, which is between about 1.3 and 1.55. Thus, while it may be desirable in dermatologic and cosmetic applications to have a device with an antimicrobial surface such as TiO2 in general, the presence of such skin contacting materials necessarily compromises the delivery of light to the skin.